theres more to tanking then just knowing your rotation, a big part is knowing the monsters/bosses and their abilities/mechanics. Mainly boss fights, you need to know positioning, timing, and what cooldowns to use and when. The role requires alot more strategy and knowledge than the others. It sounds like you have yet to reach level 30 and unlock Paladin so you don't have to worry about alot of that yet, but turning the bosses away from group is generally just a good habit to get into, as well as tanking by the edge of the arena most times, not all.